It's tough to do, getting the right pair. And there are so many variables.

Tip #1, you have to know your own shape. This requires careful introspection. What do you look like right now?  Not plus or minus 20 lbs. 
Tip #2, If this initial step proves to be difficult, get someone to help you. CHOOSE WELL! Go with someone you really know and trust. Really, take your time and get this one right. And go ahead, take your measurements. It is important. Muy importante.
*Oh, and don't be so hard on yourself. It does you No Good!

What is your best look? Are you low rider or a tummy tucker? Long legs or short? Flare leg or tapered? Some girls go "curvy," which is to say: generally a regular size jean with a generous butt section. The thigh and butt measurements are crucial to a good fit and overall satisfaction, so get those measurements right.

That brings us to the place where there are so many choices, too many really. So let's try a few things. Look around at what others are wearing and how they are wearing it. So many of us wear jeans that don't really fit. It is unfortunate, but it doesn't have to be you!  I think this brings us back to knowing who and what we are, but there is more. I won't over-simplify.

Tip #3 Look for someone your size who does it right. They got style. You see them. Walk right up and tell this person that he or she looks really good, and ask them what they're wearing. You'll so make their day. If I'm wrong here, I'll apologize, but I won't have to. People love to go on about themselves. If that's too much, snoop heavily. What the hell is he/she wearing? Moderate to expensive jeans leave their Branding littered all over the street. Check people out and retain every last detail. Are they up to her chest or down to her knees. Tight on the thigh? Dragging, or up on the ankle.

Really though, I'm supposed to be helping you make your best online decision, because buying jeans online is really tough. You have to know your size, shape, and flavor. Then, you have to be able to order the best available pair of jeans without ever trying them on. Yeah, that's tough. 

Tip #4 Buying online requires time and patience. You have to go through a lot of listings.
 The dealer is the most important detail in your discovery.
Can you make a fair deal with this dealer? Yes, you are looking for jeans, but really, the right jeans dealer is paramount. Does the dealer know what he is selling? How many successful transactions? Return policy? Customer service? Get your questions answered! Are the pictures good? Is the listing consistent or are there discrepancies? Get clarification. How responsive? How long does it take to get the product? Too many I don't or I won't or you musts- Move On. I say: Demand service!

Many Ebay sellers have pages and pages of rules and disclaimer. When I see this I move away. I look for someone who answers my questions promptly, no matter how inane, and stands behind the product. I like a concise listing. What are you getting exactly? How will it arrive? How do you pay?
Tip #5 Free Shipping is nice. Not because it is free (nothing is), but because you know exactly what you're in for.

The customers is always right. Do you really need a tip # on that one?  The problem here is uninformed, timid, and insecure customers (who don't know what they want or how to get it), and of course, generally lazy dealers. Tip #6 Only an activist customer gets more. 

Tip #7Go to the mall. Try on a bunch of expensive, quality clothes and buy nothing. Keep careful notes instead. Go home and shop those same styles online and know what you know. Trtade the urge for immediate gratification for cold hard cash.  You won't belive your own results.

And finally, Tip #8, go to your own wardrobe, your perfect pair, and, assuming they fit, reorder right here and now. Don't throw away your ruined, old favorites without at least writing down all the details. Replace what works for you. Right now there are 142,778 pairs of jeans available on Ebay. There's one for you.